OTHER COMPREHENSIVE INCOME (LOSS) Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Net unrealized gains on available-for-sale securities, beginning balance	$ 11,801	$ 22,180	$ 29,310	$ 3,250
Net unrealized losses on cash flow hedging derivative instruments, beginning balance	538	(6,802)	(4,626)	(6,048)
Net unrecognized gains on postretirement plans, beginning balance	(3,774)	(3,337)	(3,944)	(3,470)
Accumulated other comprehensive (income) loss, beginning balance	8,565	12,041	20,740	(6,268)
Net Unrealized Gains (Losses) on AFS Securities
Other comprehensive income (loss) before reclassifications	2,296	7,130	(15,213)	26,060
Less: Amounts reclassified from AOCI	0	0	0	0
Other comprehensive income (loss)	2,296	7,130	(15,213)	26,060
Net Unrealized Losses on Cash Flow Hedges
Other comprehensive income (loss) before reclassifications	(2,514)	31	2,504	(871)
Less: Amounts reclassified from AOCI	(150)	(21)	(296)	(169)
Other comprehensive income (loss)	(2,364)	52	2,800	(702)
Defined Benefit Postretirement Plans
Other comprehensive income (loss) before reclassifications	175	137	350	275
Less: Amounts reclassified from AOCI	4	4	9	9
Other comprehensive income (loss)	171	133	341	266
Accumulated other comprehensive Income (Loss)
Other comprehensive income (loss) before reclassification	(43)	7,298	(12,359)	25,464
Less: Amounts reclassified from AOCI	(146)	(17)	(287)	(160)
Other Comprehensive Income (Loss)	103	7,315	(12,072)	25,624
Net unrealized gains on available-for-sale securities, ending balance	14,097	29,310	14,097	29,310
Net unrealized losses on cash flow hedging derivative instruments, ending balance	(1,826)	(6,750)	(1,826)	(6,750)
Net unrecognized gains on postretirement plans, ending balance	(3,603)	(3,204)	(3,603)	(3,204)
Accumulated other comprehensive (income) loss, ending balance	$ 8,668	$ 19,356	$ 8,668	$ 19,356